In the mating disruption for controlling the emergence density of insects through release of, for example, a sex pheromone at a constant concentration for a long period of time, it is required to gradually release a volatile chemical to ensure a long lasting effect thereof. The mating disruption means a method for disturbing mating of the insects by emitting a sex pheromone in fields at a concentration substantially higher than that released by insects so as to lower the communication ability of the insects such as an ability of male or female insects to recognize the individual opposite sex or to confirm the positions thereof. For the mating disruption, a sustained release preparation containing a sex pheromone of a insect is used.
The sustained release preparation has already been industrialized and commercially available. A sustained release preparation having a sex pheromone filled in a plastic capillary tube has become the mainstream owing to high stability of its performance (Patent Document 1).
However, the plastic capillary tube has a problem that a decrease in the amount of a liquid remaining in the tube as a result of release may lead to a reduction in the release area and thus a reduction in the release amount in the latter half of the release. With a view to overcoming the above-described problem, there has been proposed a plastic container comprising an porous inner layer which has pores communicated to each other and an outer layer having a similar quality to the inner layer (Patent Document 2).
Patent Document 1: Japanese Patent Application                Unexamined Publication No. 57-156403/1982        
Patent Document 2: Japanese Patent Application                Unexamined Publication No. 7-313035/1995        